The incidence of premature coronary atherosclerosis in the human population. Highly correlated to decreased concentrations of high density lipoprotein or its major apolipoprotein A-I, this condition is referred to as hypoalphalipoproteinemia. The goal of the studies proposed in this application are to elucidate the molecular mechanisms which are responsible for regulating the production of high density lipoproteins at the level of apo-A-I gene expression. In order to clearly define differences based on apo A-I gene expression and to relate these differences to variation in apo A- I production, a recently described model system will be used. It is well established that the African green monkey develops a less severe hypercholesterolemia and atherosclerosis than the cynomolgus monkey when fed levels of cholesterol and fat resembling the North American diet. An important feature of this difference is that African green monkeys have a substantially higher (3 fold) level of plasma HDL and apo A-I concentration than cynomolgus monkeys, factors which may contribute to their greater ability to resist the development of atherosclerosis. Furthermore, apo A-I mRNA abundance in both the liver and small intestine have been found to correlate with the level of hepatic apo A-I production and apo A- I plasma concentration for both the African green and cynomolgus monkey. The studies proposed in this application, therefore, will seek to determine if this species-specific difference in the levels of tissue apo A-I mRNA reflect differences in the regulation and expression of the primate apo A-I gene. To do this, the apo A-I gene will be isolated and sequenced from both African green and cynomolgus monkeys. The degree of sequence homology between the two species will be compared, as well as to the human apo A-I gene sequence. Relative rates of apo A-I transcription will be measured and, the apo A-I mRNA steady state abundance measurements will be correlated to the rates of apo A-I gene transcription for liver and small intestine in both species. 5'flanking sequences of the apo A-I gene for both the African green and cynomolgus monkey will be analyzed by deletion mapping analysis to identify regulatory elements which responsible for species-specific expression of the primate apo A-I gene. The entire apo A-I gene cluster will be investigated in both primate species to determine whether apo A-I, apo C-III and apo A-VI exists as a multi-gene family. The knowledge gained by the completion of these studies will be used to develop strategies for the treatment of hypoalphalipoproteinemia and coronary heart disease.